Modern computing devices (e.g., desktop computers, laptops, netbooks, tablets, smartphones, etc.) can generally operate in one of a plurality of power modes or power states. These power modes may range from a “working” power mode, in which the computing device is fully powered and operational, to an “off” power mode in which the device is fully powered down and non-operational. Traditionally this “working” power mode is the default operating mode of computing devices. However, there are power modes between these two power modes (working and off) that trade-off performance characteristics of some functions in exchange for power savings or reduced power consumption.
For example, a low-power state of a computing device may be referred to as “Standby,” “Sleep,” “Suspend to RAM,” “Suspend to Memory,” or “Suspend.” Advanced Configuration and Power Interface (ACPI) power state S3. In such a low-power state, aside from powering the random access memory (“RAM”) that is required to restore the computing device's state, the computing device attempts to reduce or cut power to all unneeded parts of the machine (e.g., the hard disk(s) stop spinning, the display device is placed into a dark or low-power state, and peripheral devices are de-powered). Such a low-power state often is called Stand By (for computing devices running a Microsoft Windows 95—Server 2003 operating system), or is called Sleep (for computing devices running an Apple operating system or a Windows Vista, Windows 7, Windows Server 2008 operating system), or Suspend (for computing devices running a Linux operating system). In such a state, the processing functions of the computing device are powered down, and some small amount of power is used to preserve the contents of RAM and support waking up the computing device from the low-power state into the normal, working, or full power state.
When the computing device is placed into the Standby, Sleep, or Suspend to RAM state, it typically consumes less than about 20% of the total power than is consumed with the device is in the working or full power mode. However, while power consumption is greatly reduced compared to the Working power mode, the Sleep power mode requires that power be constantly supplied and consumed in order to power or refresh the volatile memory (e.g., RAM) lest the operating state be erased from the volatile memory.
In another example implementation, a low-power state of the computing device may be referred to as “Hibernate,” “Hibernation,” “Safe Sleep,” “Suspend to Disk,” “Suspend to File,” or ACPI power state S4. In such a state the contents of the computing device's RAM are written to non-volatile storage such as a hard disk, as a file or on a separate partition, before powering off the computing device. When the computing device is restarted it reloads the data that had been written to the non-volatile memory and is restored to the state it was in when hibernation was invoked. To enable hibernation, the hard disk must have sufficient free space to store all non-replaceable contents of RAM.
Such a low-power state often is called Hibernate (for computing devices running a Microsoft Windows 95—Server 2003, and Windows 7 operating system), Fast Sleep (for computing devices running a Microsoft Vista operating system), Safe Sleep (for computing devices running an Apple operating system), or Suspend to Disk (for computing devices running a Linux operating system). When the computing device is placed into the Hibernate, Safe Sleep, or Suspend to Disk state, it typically consumes about as much power as is consumed when the device is powered off. Hibernating and later restarting is usually faster than closing down, later starting up, and starting all the programs that were running.